I'm very curious why Puzzle Agent 2 isn't available on the Mac on steam. It seems uncharacteristic of Telltale, especially since there is a mac version on the telltale site.
I'm going to purchase it either way, but to be honest its a little disappointing. I'm hoping this is just a mistake, or temporary release. Maybe the Mac compatability will be added to the Steam version later.
Perhaps a bug is holding back it's compatability?